Method and apparatus for combusting fuel within a gas turbine engine

ABSTRACT

A nozzle for channeling a fluid into a combustor assembly. The nozzle includes a body including a centerline, a first passageway extending through the body along the centerline, and a nozzle tip coupled to a downstream end of the first passageway. The nozzle tip has a radius extending from a center of the nozzle tip to an outer surface of the nozzle tip. The nozzle tip includes a downstream face, and a plurality of outlet passageways that each include an opening defined in the downstream face. Each opening includes respective X-, Y-, and Z-axes defined with respect to a tangent line, the radius, and the centerline. Each of the plurality of outlet passageways is at discharge angle of greater than 30° measured with respect to the respective Z-axis in a respective X-Z plane.

BACKGROUND OF THE INVENTION

This invention relates generally to a gas turbine engine, and, morespecifically, to a combustion system for a gas turbine engine.

In at least some known gas turbine engine combustion systems, tofacilitate reducing the possibility of lean blow-out, or a blow outcaused when the environment has a low fuel to air ratio, diffusion fuelis used to start turbine operation. Depending on the turbine, diffusionfuel injected through fuel nozzles may become concentrated downstreamfrom the fuel injection nozzles. The increased concentration ofdiffusion fuel may undesirably increase a fuel rich fuel/air ratiodownstream from the fuel injection nozzles such that the fuel/air ratiois increases beyond the upper design limit. Such a fuel rich environmentmay exceed a rich blow out (RBO) boundary causing the diffusion fuelflame to blow out. More specifically, most known rich blow outs occur atabout 80% of turbine speed during turbine start up.

Some known combustion systems compensate for the fuel rich environmentby reducing the flow of diffusion fuel and injecting a fuel premixedwith air before the turbine obtains full operating speed. A turbinestart-up that injects premixed fuel before the turbine reaches fullspeed may be referred to, for example, as a “lean-lean start.” However,because the premix fuel flame is more unstable than diffusion fuelflames, to facilitate stabilizing the flame more fuel must be suppliedto a premix fuel flame than to a diffusion fuel flame. For example, insome known systems, approximately 50% or more of the total fuel injectedinto the combustor is premix fuel injected through one of the pluralityof nozzles within the combustor.

In at least some known combustors, a lean-lean start may increase thelocal liner wall temperature near the premix fuel flame. Such anincrease in temperature generally occurs because of the disproportionateamount of premixed fuel supplied to one of the fuel nozzles, as comparedto the amount of fuel supplied to other nozzles within the combustor.Moreover, such an increase in temperature may prematurely wear thecombustor hardware surrounding the flame, such as, for example, thecombustor liner and/or transition pieces. As a result, such combustorhardware may be replaced more frequently than if the start-up combustiontemperatures were maintained at a lower temperature. To compensate forhigher temperatures, some known combustors include components that aremore resistant to thermal wear. Such components may add cost and/orweight to the engine compared to engines having combustors that do notinclude thermally resistant components.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for operating a gas turbine engine including acombustor assembly is provided. The method includes channeling a firstfluid through a first nozzle into the combustor assembly, igniting thefirst fluid within the combustor assembly downstream from the firstnozzle, channeling a second fluid through a second nozzle into thecombustion assembly when the gas turbine engine attains a speed ofgreater than 85% of rated speed, igniting the second fluid within thecombustor assembly downstream from the second nozzle, terminating a flowof the first fluid through the first nozzle, and channeling the secondfluid to the first nozzle.

In another aspect, a nozzle for channeling a fluid into a combustorassembly is provided. The nozzle includes a body including a centerline,a first passageway extending through the body along the centerline, anda nozzle tip coupled to a downstream end of the first passageway. Thenozzle tip has a radius extending from a center of the nozzle tip to anouter surface of the nozzle tip. The nozzle tip includes a downstreamface, and a plurality of outlet passageways that each include an openingdefined in the downstream face. Each opening includes respective X-, Y-,and Z-axes defined with respect to a tangent line, the radius, and thecenterline. Each of the plurality of outlet passageways is at dischargeangle of greater than 30° measured with respect to the respective Z-axisin a respective X-Z plane.

In still another aspect, a combustor assembly for use with a gas turbineengine is provided. The system includes a plurality of first nozzlescoupled to the combustor assembly. Each of the first nozzles includes anozzle tip having a plurality of outlet passageways coupled to a firstfuel source. Each of the first nozzles further includes a plurality offirst vane passageways coupled to a second fuel source. The systemfurther includes a second nozzle coupled to the combustor assembly. Thesecond nozzle includes a plurality of second vane passageways coupled tothe second fuel source. The system includes a control system coupled tothe combustor assembly. The control system is configured to channel afirst fuel from the first fuel source through the outlet passageways ofthe first nozzles, and to channel a second fuel from the second fuelsource through the second vane passageways of the second nozzle when thegas turbine engine attains a speed of greater than 85% of rated speed.The control system is further configured to channel the second fuel fromthe second fuel source through the plurality of first vane passagewaysof the plurality of first nozzles when the gas turbine engine is at aload of greater than a first predetermined percentage of a baseload, andto reduce a flow of the first fuel entering the plurality of firstnozzles when the gas turbine engine is at a load of greater than thefirst predetermined percentage of the baseload.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is partial cross-sectional view of an exemplary gas turbinecombustion system.

FIG. 2 is a schematic side view of a portion of the combustion systemshown in FIG. 1.

FIG. 3 is front view of the combustion system shown in FIG. 2.

FIG. 4 is a cross-sectional view of an exemplary fuel nozzle assemblythat may be used with the combustion system shown in FIG. 1.

FIG. 5 is a perspective view of an exemplary fuel nozzle tip that may beused with the fuel nozzle shown in FIG. 4.

FIG. 6 is a cross-sectional view of the fuel nozzle tip shown in FIG. 5.

FIG. 7 is a flowchart of an exemplary method of operating the combustionsystem shown in FIG. 1.

FIG. 8 is a graphical representation illustrating exemplary fuel circuitproportions that may be used when using the method shown in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is partial cross-sectional view of an exemplary gas turbineengine 10 that includes a plurality of fuel nozzle assemblies 400. FIG.2 is a schematic side view of a portion of gas turbine engine 10. FIG. 3is front view of the portion of gas turbine engine 10 shown in FIG. 2.

Gas turbine engine 10 includes a compressor 12, a combustor 14, and aturbine 16. Only a first stage nozzle 18 of turbine 16 is shown inFIG. 1. In the exemplary embodiment, turbine 16 is drivingly coupled tocompressor 12 with rotors (not shown) that are connected by a singlecommon shaft (not shown). Compressor 12 pressurizes inlet air 20 whichis then channeled to combustor 14 where it cools combustor 14 andprovides air to the combustion process. More specifically, air 22channeled to combustor flows in a direction generally opposite to theflow of air through engine 10. In the exemplary embodiment, gas turbineengine 10 includes a plurality of combustors 14 orientedcircumferentially about engine casing 24. More specifically, in theexemplary embodiment, combustors 14 are, for example, but are notlimited to being, can-annular combustors.

In the exemplary embodiment, engine 10 includes a double-walledtransition duct 26. More specifically, in the exemplary embodiment,transition duct 26 extends between an outlet end 28 of each combustor 14and the inlet end 30 of turbine 16 to channel combustion gases 32 intoturbine 16. Further, in the exemplary embodiment, each combustor 14includes a substantially cylindrical combustor casing 34. Combustorcasing 34 is coupled at an open aft end 36 to engine casing 24.Combustor casing 34 may be coupled to engine casing 24 using, forexample, but not limited to using, bolts 38, mechanical fasteners (notshown), welding, and/or any other suitable coupling means that enablesengine 10 to function as described herein. In the exemplary embodiment,a forward end 40 of combustor casing 34 is coupled to an end coverassembly 42. End cover assembly 42 includes, for example, supply tubes,manifolds, valves for channeling gaseous fuel, liquid fuel, air and/orwater to the combustor, and/or any other components that enable engine10 to function as described herein. In the exemplary embodiment, thecomponents within end cover assembly 42 are coupled to a control system44 for controlling at least the air and fuel entering combustor 14, asdescribed in more detail below. Control system 44 may be, for example,but is not limited to being, a computer system and/or any other systemthat enables combustor 14 to function as described herein.

In the exemplary embodiment, a substantially cylindrical flow sleeve 46is coupled within combustor casing 34 such that sleeve 46 issubstantially concentrically aligned with casing 34. Flow sleeve 46 iscoupled at an aft end 48 to an outer wall 50 of transition duct 26 andcoupled at a forward end 52 to combustor casing 34. More specifically,in the exemplary embodiment, forward end 52 is coupled to combustorcasing 34 by, for example, coupling a radial flange 54 of sleeve 46 tocombustor casing 34 at a butt joint 56 such that a forward section 58and an aft section 60 of casing 34 are coupled against each other.Alternatively, sleeve 46 may be coupled to casing 34 and/or transitionduct 26 using any other suitable coupling assembly that enables engine10 to function as described herein.

Flow sleeve 46, in the exemplary embodiment, includes a combustion liner62 coupled therein. Combustion liner 62 is aligned substantiallyconcentrically within flow sleeve 46 such that an aft end 64 is coupledto an inner wall 66 of transition duct 26, and such that a forward end68 is coupled to a combustion liner cap assembly 70. Combustion linercap assembly 70 is secured within combustor casing 34 by a plurality ofstruts 72 and an associated mounting assembly (not shown). In theexemplary embodiment, an air passage 74 is defined between liner 62 andflow sleeve 46, and between transition duct inner and outer walls 66 and50. Transition duct outer wall 50 includes a plurality of apertures 76defined therein that enable compressed air 20 from compressor 12 toenter air passage 74. In the exemplary embodiment, air 22 flows in adirection opposite to a direction of core flow (not shown) fromcompressor 12 towards end cover assembly 42. Further, in the exemplaryembodiment, combustor 14 also includes a plurality of spark plugs 78 anda plurality of cross-fire tubes 80. Spark plugs 78 and cross-fire tubes80 extend through ports (not shown) in liner 62 that are defineddownstream from combustion liner cap assembly 70 within a combustionzone 82. Spark plugs 78 and cross-fire tubes 80 ignite fuel and airwithin each combustor 14 to create combustion gases 32.

In the exemplary embodiment, a plurality of fuel nozzle assemblies 400are coupled to end cover assembly 42. More specifically, in theexemplary embodiment, combustor 14 includes five nozzle assemblies 400.Alternatively, combustor 14 may include more or less than five fuelnozzle assemblies 400. In the exemplary embodiment, fuel nozzleassemblies 400 are arranged in a generally circular array about acenterline 84 of combustor 14. Alternatively, fuel nozzle assemblies 400may be arranged in a non-circular array. Although, only one type of fuelnozzle assembly 400 is described herein, more than one type of nozzleassembly, or any other type of fuel nozzle, may be included in combustor14. Further, in the exemplary embodiment, combustor 14 includes aplurality of quaternary pegs 86 that extend radially inward fromcombustor casing 34 and substantially circumscribe fuel nozzleassemblies 400. Although the exemplary embodiment includes quaternarypegs 86, other embodiments may not include quaternary pegs 86.

Combustion liner cap assembly 70 includes a plurality of premix tubeassemblies 88. In the exemplary embodiment, each premix tube assembly 88substantially circumscribes each fuel nozzle assembly 400, and as such,the number of premix tube assemblies 88 is equal to the number of nozzleassemblies 400. Alternatively, the number of premix tube assemblies 88may be greater than, or less than, the number of nozzle assemblies 400.In the exemplary embodiment, each premix tube assembly 88 extendspartially into combustion liner cap assembly 70 such that premix tubeassemblies 88 are coupled to an aft support plate 90 and to a forwardsupport plate 92. More specifically, an aft end 91 of each premix tubeassembly 88 extends through openings (not shown) in aft plate 90 and aforward end 93 of premix tube assembly 88 extends through openings (notshown) in plate 92.

In the exemplary embodiment, forward support covers (not shown) areincluded and are each coupled to support plate 92. The support coversfacilitate securing plate 92 of each of premix tube assemblies 88 tocombustor 14. Further, aft plate 90 may be an impingement plate thatincludes an array of effusion cooling apertures (not shown), and thatmay be shielded from the thermal heat generated by of the combustorflame by shield plates (not shown). In the exemplary embodiment, eachpremix tube assembly 88 includes an assembly including two tubes (notshown) that are separated by a premix tube hula seal (not shown). Thehula seal enables the dual-tube assembly to thermally expand andcontract as combustion liner cap assembly 70 expands during operatingconditions. Thus, as the distance between plates 92 and 90 changes dueto thermal expansion, premix tube assemblies 88 are free to expandaccordingly along an axis of symmetry (not shown).

Plate 92, in the exemplary embodiment, is coupled to a plurality offorwardly-extending floating collars (not shown). The collars aresubstantially concentrically aligned with each of the openings definedin plate 92 such that each premix tube assembly 88 includes one collar.Alternatively, each premix tube assembly 88 may include more or lessthan one collar. In the exemplary embodiment, each collar supports anair swirler (not shown), which may be, for example, positioned adjacentto a radially outermost wall (not shown) of each fuel nozzle assembly400, formed integrally with each nozzle assembly 400, and/or configuredin any other suitable configuration that enables engine 10 to functionas described herein. The arrangement of swirlers is such that air 22flowing through air passage 74 is forced to reverse direction at acombustor inlet end 94 of combustor 14 (between end cover assembly 42and combustion liner cap assembly 70) and to flow through the airswirlers and premix tube assemblies 88. Fuel passages (not shown) ineach of the air swirlers channel fuel through an arrangement ofapertures that continuously introduce gaseous fuel, depending upon theoperational mode of gas turbine engine 10, into the passing air 22 tocreate a fuel and air mixture that is ignited in combustion burning zone82 and downstream from premix tube assemblies 88.

In the exemplary embodiment, combustor 14 includes four fuel circuits200, 202, 204, and 206, that are coupled to a fuel supply 208 and tocontrol system 44. Although only one fuel supply 208 is shown anddescribed, engine 10 may include more than one fuel supply 208.Moreover, fuel supply 208 may include a plurality of types of fuel.Specifically, in the exemplary embodiment, combustor 14 includes aprimary fuel circuit 200, a secondary fuel circuit 202, a tertiary fuelcircuit 204, and a quaternary fuel circuit 206. Alternatively, combustor14 may include more or less than four fuel circuits 200, 202, 204,and/or 206. In the exemplary embodiment, primary fuel circuit 200includes a primary circuit inlet 210 to supply fuel, for example,diffusion fuel 212, to primary fuel circuit 200. Secondary fuel circuit202 includes a secondary circuit inlet 214 to supply fuel, for example,premix fuel 216, to secondary fuel circuit 202. Similarly, tertiary fuelcircuit 204 includes a tertiary circuit inlet 218 to supply fuel, forexample, premix fuel 216, to tertiary fuel circuit 204. Quaternary fuelcircuit 206 includes a quaternary circuit inlet 228 to supply fuel, forexample, premix fuel 230, to quaternary fuel circuit 206.

In the exemplary embodiment, combustor 14 also includes a purge aircircuit 220 having a purge air circuit inlet 222 used to supply air 224to at least one fuel nozzle assembly 400 from an air supply 226, asdescribed in more detail below. In the exemplary embodiment, air supply226 includes air 22 channeled from air passage 74. Alternatively, airsupply 226 may supply air from any other suitable supply of air, suchas, for example, ambient air. Purge air circuit 220 is coupled tocontrol system 44. In the exemplary embodiment, premix fuel 216 andpremix fuel 230 have generally similar compositions. Alternatively,premix fuel 230 may have a composition that is different than thecomposition of premix fuel 216. Moreover, as used herein, the term“premix fuel” refers to fuel, which may be gaseous, liquid, orpulverized solid fuel, that is mixed with air prior to enteringcombustion zone 82. Further, as used herein, the term “diffusion fuel”refers to fuel, which may be gaseous, liquid, or pulverized solid fuel,that is not mixed with air prior to entering combustion zone 82.

In the exemplary embodiment, four of the five fuel nozzle assemblies 400are primary fuel nozzle assemblies 402 and are coupled to primary fuelcircuit 200 and to secondary fuel circuit 202, and the remaining fuelnozzle assembly 400 is a tertiary fuel nozzle assembly 404 that iscoupled to tertiary fuel circuit 204 and purge air circuit 220. Eachquaternary peg 86 is coupled to quaternary fuel circuit 206. Further, inthe exemplary embodiment, each fuel circuit 200, 202, 204, and 206includes a respective valve V₁, V₂, V₃, and V₄ used to control fuel flowinto each circuit 200, 202, 204, and/or 206. Purge air circuit 220includes a valve VA used to control the air flow into circuit 220. Morespecifically, in the exemplary embodiment, valve V₁ controls an amountof diffusion fuel 212 entering primary fuel circuit 200, valve V₂controls a flow of premix fuel 216 into secondary fuel circuit 202,valve V₃ controls a flow of premix fuel 216 into tertiary fuel circuit204, and valve V₄ controls an amount of premix fuel 230 enteringquaternary fuel circuit 206. In an alternative embodiment, a premixvalve (not shown) is coupled to both secondary and tertiary fuelcircuits 202 and 204 to control a flow of premix fuel 216 into valves V₂and V₃ from fuel supply 208. In the exemplary embodiment, fuel circuits200, 202, 204, and 206 are coupled to control system 44 to control fuelflow to circuits 200, 202, 204, and 206, and to fuel nozzle assemblies400. More specifically, control system 44 may control fuel flow by, forexample, but not limited to, controlling valves V₁, V₂, V₃, and V₄.Similarly, purge air circuit valve VA is coupled to control system 44such that a purge air flow may be regulated.

In operation, air 20 enters engine 10 through an inlet (not shown) andis compressed in compressor 12. Compressed air 20 is discharged fromcompressor 12 and is channeled to combustor 14. Air 20 enters combustorthrough apertures 76 and then flows through air passage 74 towards endcover assembly 42 of combustor 14. Air 22 flowing through air passage 74is forced to reverse its flow direction at combustor inlet end 94 and isredirected through the air swirlers and premix tube assemblies 88. Fuel212, 216, and/or 230 is supplied into combustor 14 through end coverassembly 42. Control system 44 regulates the air 22 and/or 224 and fuel212, 216, and/or 230 supplied to nozzle assemblies 400 and/or premixtube assemblies 88, as described in more detail below. Ignition isinitially achieved when control system 44 initiates a starting sequenceof gas turbine engine 10, and spark plugs 78 are retracted fromcombustion burning zone 82 once a flame has been continuouslyestablished. At the opposite end of combustion burning zone 82, hotcombustion gases 32 are channeled through transition duct 26 and turbinenozzle 18 towards turbine 16.

FIG. 4 is a cross-sectional view of an exemplary fuel nozzle assembly400 that may be used with combustor 14. For exemplary purposes, primaryfuel nozzle assembly 402 will be described, but it will be understoodthat tertiary fuel nozzle assembly 404 is essentially similar to primaryfuel nozzle assembly 402, except that purge air 224, rather thandiffusion fuel 212, is supplied to tertiary fuel nozzle assembly 404. Inthe exemplary embodiment, tertiary fuel nozzle assembly 404 isconfigured to inject premix fuel 216 in a manner that is substantiallysimilar to the primary fuel nozzle 402 premix fuel 216 injectionconfiguration.

In the exemplary embodiment, each fuel nozzle assembly 402 includes abody 406, a base 408, and a vane assembly 410. Body 406 extends axiallyalong a nozzle centerline 412. Body 406 is formed with a plurality ofpassages 414, 416, and 418 that each extend substantially parallel tocenterline 412 from a tip end 420 through base 408 to a base end 422.More specifically, in the exemplary embodiment, nozzle assembly 402includes a center passage 414, a diffusion passage 416, and a premixpassage 418.

In the exemplary embodiment, center passage 414 includes an oil/watercartridge (not shown) and is formed with an outlet 424 through a nozzletip 500, and diffusion passage 416 includes a diffusion nozzle inlet426. Tertiary fuel nozzle assembly 404 includes a purge air passage (notshown), including a nozzle purge air inlet (not shown) that are eachconfigured substantially similarly to diffusion passage 416 anddiffusion nozzle inlet 426, except that the purge air inlet is coupledto purge air circuit 220. Diffusion passage 416 includes a plurality ofdiffusion outlets 502 that extend through nozzle tip 500, as describedin more detail below. Premix passage 418, included in both primary andtertiary fuel nozzle assemblies 402 and 404, includes a premix fuelinlet 428 defined in base 408. Premix passage 418 includes a pluralityof radially, outwardly-extending vane passages 430. More specifically,in the exemplary embodiment, vane passages 430 each extend through avane 432 (shown in FIG. 3) of vane assembly 410. Each vane passage 430includes a plurality of premix vane openings 434 (also shown in FIG. 3).

In the exemplary embodiment, base 408 is coupled to end cover assembly42 using, but not limited to using, a plurality of mechanical fasteners436, for example. Alternatively, base 408 is coupled to end coverassembly 42 using any other suitable fastening mechanism that enablesnozzle assembly 402 and/or 404 to function as described herein. In theexemplary embodiment, diffusion passage 416 is coupled in flowcommunication with primary fuel circuit 200. Further, in the exemplaryembodiment, within primary fuel nozzle assemblies 402, premix passage418 is coupled to secondary fuel circuit 202, and in tertiary fuelnozzle assembly 404, premix passage 418 is coupled to tertiary fuelcircuit 204.

FIG. 5 is a perspective view of an exemplary nozzle tip 500 that may beused with fuel nozzle assembly 402 and/or 404 (shown in FIG. 4). FIG. 6is a cross-sectional view of nozzle tip 500. In FIG. 6, center passage414 and center outlet 424 have been omitted for clarity.

In the exemplary embodiment, nozzle tip 500 includes center outlet 424and a plurality of diffusion outlets 502. For exemplary purposes,diffusion outlets 502 are described, but it should be understood that,in tertiary fuel nozzle assembly 404, purge air outlets (not shown) areessentially similar to diffusion outlets 502, except that purge air,rather than diffusion fuel, is supplied through the purge air outlets.In the exemplary embodiment, a forward face 504 of nozzle tip 500includes a central sloped portion 506 and an annular recessed portion508. Recessed portion 508 is substantially annular and includes aradially inner wall 510 and a radially outer wall 512 that are orientedwith respect to each such that recessed portion 508 has a generallyV-shaped cross-sectional profile. In the exemplary embodiment, recessedportion 508 is oriented to avoid the flow of diffusion fuel 212 (shownin FIG. 2) exiting diffusion outlets 502. Alternatively, recessedportion 508 may be oriented to direct the flow of diffusion fuel 212(shown in FIG. 2) exiting diffusion outlets 502.

In the exemplary embodiment, center outlet 424 extends through nozzletip 500 generally along an axial centerline 514. Each diffusion outlet502 includes a forward opening 516 and an aft opening 518, and outlet502 extends between openings 516 and 518. In the exemplary embodiment,forward openings 516 are each located at a radius R from centerline 514,in a substantially circular array. More specifically, in the exemplaryembodiment, forward openings 516 are each defined in radially inner wall510 and have a diameter D. In the exemplary embodiment, diameter D islarger than 0.110 inches, and more specifically, may be, for example,0.126 inches.

A respective coordinate system is defined at each forward opening 516.In the exemplary embodiment, an X-axis is aligned tangentially to acircle having a radius R, a Y-axis is aligned perpendicularly to theX-axis in a radial direction, and a Z-axis is substantially aligned withcenterline 514. An angle α is measured from the Z-axis in an X-Z plane,and an angle β is measured from the Z-axis in a Y-Z plane. In theexemplary embodiment, each diffusion outlet 502 is oriented along arespective line F that extends from each respective forward opening 516at angle α and at angle β. As such, diffusion outlets 502 are defined ina helical array in nozzle tip 500. In the exemplary embodiment, angle αis substantially equal to angle β. Alternatively, angle α may bedifferent than angle β. Further, in the exemplary embodiment, both angleα and angle β are greater than approximately 30°. More specifically, inone exemplary embodiment, angle α and angle β are both approximatelyequal to 45° such that the fuel flow immediately downstream from fuelnozzle assemblies 400 is lean enough to ignite and to sustaincombustion.

When combustor 14 is in operation, diffusion fuel 212 is channeled fromfuel supply 208 through primary fuel circuit 200 and primary fuel nozzleassemblies 402 into combustion zone 82. More specifically, controlsystem 44 controls the operation of valve V₁ to enable diffusion fuel212 to enter primary fuel circuit 200. Diffusion fuel 212 is dischargedfrom primary fuel circuit 200 into primary nozzle assemblies 402 throughdiffusion circuit and nozzle inlets 210 and 426. Diffusion fuel 212 isdischarged from primary nozzle assemblies 402 through each nozzle tip500. Diffusion outlets 502 ensure the diffusion fuel 212 is dischargedat angles α and β and generally along each line F. As such, diffusionfuel 212 diffuses adjacent each nozzle assembly tip end 420 and remainslean enough to ignite. Diffusion fuel 212 is dispersed within combustionzone 82 and mixes with air 22 entering combustion zone 82 through airpassage 74 and/or premix assemblies 88. Spark plugs 78 and cross-firetubes 80 ignite the fuel-air mixture within combustion zone 82 to createcombustion gases 32.

FIG. 7 is a flowchart of an exemplary method of operating gas turbineengine that includes primary fuel nozzle assemblies 402 and tertiaryfuel nozzle assembly 404, as described above. FIG. 8 is a graphicalrepresentation 800 of exemplary fuel circuit proportions, in percentage,with respect to mean firing temperature (TTRF), in degrees Fahrenheit,that may be used when the method illustrated in FIG. 7 is implemented.As used herein, the circuit proportions are represented using theconvention P/S/T-Q, wherein P is the approximate percentage of totalfuel within zone 82 (shown in FIG. 1) injected through primary fuelcircuit 200 (shown in FIG. 2), S is the approximate percentage of totalfuel injected through secondary and tertiary fuel circuits 202 and 204(each shown in FIG. 2) with respect to secondary fuel circuit 202, T isthe approximate percentage of total fuel injected through secondary andtertiary fuel circuits 202 and 204 with respect to tertiary fuel circuit204, and Q is the approximate percentage of total fuel within zone 82injected through quaternary fuel circuit 206 (shown in FIG. 2). P isrepresented on graph 800 as line 802, S is represented on graph 800 asline 804, T is represented on graph 800 as line 806, and Q isrepresented on graph 800 as line 808.

In the exemplary embodiment, to begin operation of engine 10, anair-fuel mixture is ignited within combustor 14. Control system 44controls a flow of fuel 212, 216, and/or 230 to combustor 14 via fuelcircuits 200, 202, 204, and/or 206. The ignition procedure is initiated700 by introducing a flow of diffusion fuel 212 into combustion zone 82.More specifically, valve V₁ is opened to enable diffusion fuel 212 toenter primary fuel circuit 200 and to flow through primary fuel nozzleassemblies 402, prior to being discharged through diffusion outlets 502into combustion zone 82. In the exemplary embodiment, primary fuelcircuit 200 supplies approximately 100% of the fuel entering combustionzone 82 during this stage of engine operation such that the fuelproportion is approximately 100/0/0-0.

Diffusion fuel 212 is ignited 702, by, for example, control system 44prompting spark plugs 78 and cross-fire tubes 80 to ignite diffusionfuel 212 within combustion zone 82. Once diffusion fuel 212 is ignited702, combustion gases 32 generated are channeled from combustion zone 82through transition duct 26 towards turbine 16. When turbine 16 attains afull-speed, no-load (FSNL) operating condition, combustor 14 is at amean firing temperature (TTRF) of, for example, 1280° F. As such,combustor 14 combusts diffusion fuel 212 from ignition through FSNL toan initial predetermined percentage of baseload without the addition ofpremix fuel 216 and/or 230 in combustion zone 82. Such an ignition maybe referred to as a “diffusion start” mode 810.

After FSNL is reached, engine 10 begins taking on load, and controlsystem 44 alters fuel flow to fuel circuits 200, 202, 204, and/or 206.More specifically, in the exemplary embodiment, prior to engine 10reaching a first predetermined percentage of baseload at a firsttransfer point 812, for example, but not limited to, a point atapproximately 1950° F. such that turbine is at substantially 30% ofbaseload, control system 44 is transferred from the diffusion start mode810 to a lean-lean mode 814. A “lean-lean mode” of operation refers to amode of turbine operation in which primary nozzle assemblies 402 supplydiffusion fuel 212 into combustion zone 82, and tertiary nozzle assembly404 supplies premix fuel 216 into combustion zone 82.

In the exemplary embodiment, the transition from the diffusion startmode 810 to the lean-lean mode 814 involves continuing a flow ofdiffusion fuel 212 to primary nozzle assemblies 402 while initiating 704a flow of premix fuel 216 to tertiary fuel nozzle assembly 404. Morespecifically, in the exemplary embodiment, control system 44 at leastpartially opens valve V₃ to enable premix fuel 216 to enter tertiaryfuel circuit 202. Alternatively, the flow of premix fuel 216 may beinitiated in any other suitable manner that enables combustor 14 tofunction as described herein. Once discharged from fuel nozzleassemblies 402 and 404, premix fuel 216 is ignited 706 by, for example,the flame generated by combusting diffusion fuel 212. In the exemplaryembodiment, during lean-lean mode 814 at a TTRF of approximately 2025°F., the fuel proportion is approximately 77/0/23-0.

As the load of engine 10 increases, the amount of premix fuel 216supplied to combustion zone 82 increases. More specifically, controlsystem 44 transitions combustor 14 from the lean-lean mode 814 to apiloted premix mode (PPM) 816 of operation at a second predeterminedpercentage of the baseload at a second transfer point 818. For example,in one embodiment, control system 44 transitions combustor 14 from thelean-lean mode 814 to PPM 816 when transfer point 818 is a point atapproximately 2100° F.

“Piloted premix mode” refers to an operating mode in which primarynozzle assemblies 402 and tertiary nozzle assembly 404 discharge premixfuel 216 into combustion zone 82, while a reduced amount of diffusionfuel 212 is discharged by primary nozzle assemblies 402. Premixoperation facilitates reducing the amount of pollutants, such as, forexample, nitrogen oxides (NOx) and/or carbon dioxide (CO), released fromfuel 212 and/or 216 during combustion by staging the air enteringcombustion zone 82. In the exemplary embodiment, an increased amount ofair within combustion zone 82 facilitates decreasing the flametemperature, or reaction temperature, which reduces thermal NOxformation within combustor 14. More specifically, air, for example, air22 from passage 74, is initially mixed with the fuel within secondaryfuel circuit 202, tertiary fuel circuit 204, and/or quaternary fuelcircuit 206 to create premix fuel 216 and/or 230. Air 22 from airpassage 74 is then mixed with premix fuel 216 in combustion zone 82.Premixing the air and fuel before the mixture is discharged intocombustion zone 82 facilitates minimizing localized fuel-rich pocketsand high temperatures within zone 82.

In the exemplary embodiment, the transition from the lean-lean mode 814to the piloted premix mode 816 involves initiating 708 a flow of premixfuel 216 to primary fuel nozzle assemblies 402, while reducing 708 aflow of diffusion fuel 212 to primary fuel nozzle assemblies 402. Such atransition generally occurs when engine 10 is operating at a secondpredetermined percentage of the base load, which is greater than thefirst predetermined percentage of the baseload. More specifically, inthe exemplary embodiment, control system 44 partially closes valve V₁and at least partially opens valve V₂ to enable premix fuel 216 to entersecondary fuel circuit 202. Alternatively, the flow of diffusion fuel212 may be reduced 708 and the flow of premix fuel 216 may be initiated708 in any other suitable way that enables combustor 14 to function asdescribed herein. Premix fuel 216 from primary fuel nozzle assemblies402 ignites, in the exemplary embodiment, from the flame generatedduring combustion of diffusion fuel 212 and/or tertiary premix fuel 216.In the exemplary embodiment, at, for example a TTRF of approximately2165° F., fuel 212 and 216 is injected through circuits 200, 202, and204 at a proportion of approximately 25/79/21-0.

As the load of engine 10 is increased, the amount of premix fuel 216supplied to combustion zone 82 increases and the amount of diffusionfuel 212 supplied to combustion zone 82 decreases. More specifically,control system 44 transitions combustor 14 from the piloted premix mode816 of operation to a premix steady state (PMSS) mode 820 of operationwhen engine 10 is at a third predetermined percentage of the baseload ata third transfer point 822. For example, in one embodiment, controlsystem 44 transitions to PMSS 820 when engine 10 is operating at apercentage of the baseload corresponding to transfer point 822 at a TTRFof approximately 2240° F.

“Premix steady state mode” refers to an operating mode in which primarynozzle assemblies 402 and tertiary nozzle assembly 404 discharge premixfuel 216 into combustion zone 82, while diffusion fuel 212 discharged byprimary nozzle assemblies 402 is terminated. The premix steady statemode 820 is substantially similar to the premix operation describedabove, except that premix steady state 820 facilitates an additionalreduction of an amount of pollutants, for example, NOx and/or CO,released from fuel 212 and/or 216 during combustion by substantiallyeliminating combustion of diffusion fuel 212.

In the exemplary embodiment, the transition from the piloted premix mode816 to the premix steady state mode 820 involves terminating 710 theflow of diffusion fuel 212 to primary fuel nozzle assemblies 402, whileincreasing a flow of premix fuel 216 to primary fuel nozzle assemblies402 when engine 10 reaches the third predetermined percentage of thebaseload. In the exemplary embodiment, a flow of premix fuel 230 toquaternary pegs 86 through quaternary fuel circuit 206 is initiated 712.The use of premix fuel 230 reduces combustion dynamics that may occur incombustor 14, such as, for example, low combustion acoustic noise and/ordynamic pressure fluctuations. In an alternative embodiment, premix fuel230 is supplied other than as described herein. In the exemplaryembodiment, control system 44 substantially closes valve V₁, opens valveV₂ to enable premix fuel 216 to enter secondary fuel circuit 202, andopens valve V₄ to enable premix fuel 230 to enter quaternary fuelcircuit 206. Alternatively, the flow of diffusion fuel 212 may beterminated and the flow of premix fuel 230 may be initiated in any othersuitable way that enables combustor 14 to function as described herein.In the exemplary embodiment, at turbine conditions of, for example, aTTRF approximately equal to 2240° F. such that turbine load is about 50%of the baseload, the fuel proportion is approximately 0/85/18-13. Atsuch a turbine condition, a turndown point may occur.

When engine 10 is operating 714 substantially at its baseload, engine 10is operating, in the exemplary embodiment, in the premix steady statemode 820. More specifically, in the exemplary embodiment, at baseload,engine 10 is at a turbine condition where a reference point 824 is at,for example, a TTRF equal to approximately 2400° F., the fuel proportionis approximately 0/82/19-8.

The above-described methods and apparatus facilitate combusting fuel ina gas turbine engine such that a maximum liner wall temperature isfacilitated to be reduced and such that a flame stability is facilitatedto be increased by improving the fuel-to-air ratio of the diffusion fueldownstream from the fuel nozzles. The ratio of fuel to air downstreamfrom the fuel nozzles remains below a rich blow out boundary byinjecting the diffusion fuel into the combustion chamber at an injectionangle that facilitates mixing the diffusion fuel with air within thecombustion chamber. Such injection of the diffusion fuel facilitateseliminating the injection of premix fuel before the turbine reachesfull-speed, no-load operation. As such, a lean-lean start is facilitatedto be avoided by injecting the diffusion fuel as described herein. Byavoiding a lean-lean start, the non-uniformity in liner wall temperatureis facilitated to be reduced, which facilitates decreasing an amount ofwear on surrounding hardware. Further, the lean-lean mode describedherein involves injecting a lower percentage of premix fuel through asingle nozzle, about 25% of total fuel in the combustor, as compared tosystems injecting about 50% of total fuel in the combustor through asingle nozzle. As such, a localized liner temperature proximate thenozzle injecting premix fuel is facilitated to be reduced.

Moreover, the diffusion fuel injection angle described hereinfacilitates forming a more stable and well-anchored flame as compared tothe generally small, unstable diffusion flames that occur during knownlean-lean starts. The more stable and well-anchored flame facilitatesreducing the possibility of a blow out, and, more specifically, a richblow out. The diffusion fuel injection angle described hereinfacilitates creating a more uniform temperature within the combustionchamber, which facilitates reducing wear on the surrounding hardware.Moreover, the diameter of the tip openings, as described herein,facilitates reducing clogging of the nozzle and facilitates increasingfuel-air mixing downstream of the fuel nozzles.

The above-described method and apparatus further facilitates stagingfuel and/or air injection which facilitates reducing the emission ofpollutants from combusting the fuel. More specifically, the fuel and/orair staging facilitates: reducing NOx and/or CO emissions as measured atan exhaust plane of the gas turbine; increasing flame stability in byusing a diffusion operating mode; maintaining fuel/air ratios between alean-blow-out margin and a rich-blow-out margin over a broad range ofgas turbine load settings; and/or decreasing combustion dynamics.

Exemplary embodiments of a method and apparatus for combusting a fuel ina gas turbine engine are described above in detail. The method andapparatus are not limited to the specific embodiments described herein,but rather, components of the method and apparatus may be utilizedindependently and separately from other components described herein. Forexample, the fuel nozzle tip may also be used in combination with othercombustion systems and methods, and is not limited to practice with onlythe gas turbine engine as described herein. Further, the method foroperating the gas turbine engine may also be used in combination withother combustion systems and methods, and is not limited to practicewith only the combustor as described herein Rather, the presentinvention can be implemented and utilized in connection with many otherfuel combustion applications.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A nozzle for channeling a fluid into a combustor assembly, saidnozzle comprising: a body including a centerline; a first passagewayextending through said body along said centerline; a second passagewayextending through said body, said second passageway substantiallycircumscribes at least a portion of said first passageway; and a nozzletip coupled to a downstream end of said first passageway and to saidsecond passageway, said nozzle tip having a radius extending from acenter of said nozzle tip to an outer surface of said nozzle tip, saidnozzle tip comprising: a downstream face; a first outlet passagewayextending through said downstream face, said first outlet passageway inflow communication with said first passageway; and a plurality of secondoutlet passageways that each comprise an opening defined in saiddownstream face, each of said plurality of second outlet passagewayshaving an inlet in flow communication with said second passageway,wherein each opening disposed radially outward from the inlet withrespect to the centerline, each opening comprises respective X-, Y-, andZ-axes defined with respect to a tangent line, said radius, and saidcenterline, each of said plurality of outlet passageways is at dischargeangle between about 30° and about 45° measured with respect to saidrespective Z-axis in a respective X-Z plane.
 2. A nozzle in accordancewith claim 1 wherein each of said plurality of second outlet passagewaysis at discharge angle of greater than 30° measured with respect to saidrespective Z-axis in a respective Y-Z plane.
 3. A nozzle in accordancewith claim 1 further comprising a third passageway extending throughsaid body, said third passageway substantially circumscribes at least aportion of said first passageway and said second passageway.
 4. A nozzlein accordance with claim 3 further comprising a plurality of vanesextending radially outward from said body, each of said plurality ofvanes comprises: a vane passageway in flow communication with said thirdpassageway; and a plurality of apertures extending from each said vanepassageway through a respective vane.
 5. A nozzle in accordance withclaim 1 wherein each said second outlet passageway opening comprises adiameter larger than substantially 0.110 inches.
 6. A nozzle inaccordance with claim 5 wherein each said second outlet passagewayopening comprises a diameter substantially equal to 0.126 inches.
 7. Anozzle in accordance with claim 1 wherein said first passagewaycomprises a fluid therein, said fluid comprises at least one of a liquidfuel, a gaseous fuel, and a solid fuel.